This invention relates to a recording/playback apparatus in which a magnetic head is fed radially of a rotating magnetic recording medium having a number of concentrically arranged circular tracks for recording a signal on a predetermined track or playing back a recorded signal from a predetermined track.
When recording on a magnetic recording medium in a recording/playback apparatus, it is necessary to create, in advance, a track map which indicates whether each track on the medium is blank or a track on which a recording has already been made. This is done in the following manner: The magnetic head is fed radially of the magnetic recording medium and processing for detecting the envelope of the recorded signal is performed at each track. If a detected envelope level is above a prescribed threshold level, a decision is rendered to the effect that the particular track is a recorded track. If the detected envelope level is below the threshold level, on the other hand, the particular track is judged to be blank. This processing is executed with regard to all of the tracks, and the results are preserved in the form of a track map.
When a recorded signal is played back from a designated track on the magnetic recording medium, the track is subjected to peak position detection processing. In playing back a still-video signal, it is desired that the best signal having little noise be read from the magnetic recording medium. In order to achieve this, it is necessary that the center of the magnetic head be made to coincide with the center of the portion of the magnetic recording medium on which the signal is actually recorded. At a recorded track on the magnetic recording medium, processing is executed for detecting the peak position of the envelope of the read signal obtained when the magnetic head is fed in the diametric direction (i.e., across the track). This is peak position detection processing and is performed by comparing detected envelope levels at neighboring envelope detection positions and moving the magnetic head in the direction of the higher envelope level.
An envelope detector circuit which detects the envelope of the signal read by the magnetic head includes an A/D converter circuit for converting the detected envelope level into a digital signal. This digital signal is applied to a controller which includes a CPU and is programmed to execute the above-described track search processing and envelope peak position detection processing.
For track search processing, it suffices merely to determine whether an envelope has been detected or whether a detected envelope exceeds a threshold level, without inquiring into the envelope level or peak position. By contrast, peak position detection processing requires comparison of detected envelope levels and therefore it is necessary to be able to distinguish between high and low levels.